Extraosseous accumulation of Tc-99m diphosphonate

Accumulation of Tc-99m diphosphonate in extraosseous tissue sometimes occurs in patients with hypercalcemia. The phenomenon is associated with microscopic and sometimes with macroscopic calcifications resulting from malignant and nonmalignant diseasa. We describe one patient with benign disease with diphosphonate accumulation in the lung region and another patient with accumulation of diphosphonate in the stomach caused by disseminated prostate cancer. The findings probably result from microcalcifications facilitated by a low intracellular pH, which occurs in the lungs and the gastric mucosa because of low carbon dioxide pressure and acid secretion, respectively.